JP5778816B1 - Solar power system - Google Patents

Abstract

An object of the present invention is to enable power generation without wasting solar energy. SOLUTION: A first solar cell 101 disposed on an incident side on which sunlight 111 from the sun 110 is incident, and a second solar cell stacked on the first solar cell 101 opposite to the incident side. Cell 102. The first solar cell 101 is composed of a first semiconductor, and the second solar cell 102 is composed of a second semiconductor having a larger band gap energy than the first semiconductor. For example, the first semiconductor is silicon and the second semiconductor is a nitride semiconductor. The second solar battery cell 102 has a smaller area than the first solar battery cell 101. In addition, a solar thermal power generation unit 103 that generates power by the heat of sunlight 112 that has passed through the first solar cells 101 around the second solar cells 102 is provided. [Selection] Figure 1

Description

  The present invention relates to a photovoltaic power generation system including a tandem solar cell in which a plurality of solar cells are joined.

  For nitride semiconductors such as GaN, materials having an energy gap in a wide range of 0.7 to 6.2 eV can be obtained by changing the mixing ratio of group III elements. This band gap range completely includes the visible light region. Taking advantage of these features, nitride semiconductors are applied to LEDs (Light Emitting Diodes) and the like, and are widely used as traffic lights and various displays.

  In addition, since the energy gap range of nitride semiconductors almost covers the spectrum of sunlight, it attracts attention as a material that can realize a solar cell with high power generation efficiency. For example, it is predicted that power generation efficiency of 31% can be expected by tandemization of a single crystal silicon solar cell and a solar cell composed of InGaN (see Non-Patent Document 1). In addition, in this prediction, it is said that a power generation efficiency of 35% can be expected by appropriately selecting the energy gap of InGaN in a three-junction cell in which two InGaN solar cells are combined with a single crystal silicon solar cell. .

  In addition, an attempt to actually manufacture a multi-junction solar cell composed of a silicon cell and a nitride semiconductor cell has also been reported (see Non-Patent Document 2).

  Thus, nitride semiconductors have a high potential for realizing ultra-high efficiency solar cells, and development of solar cells using nitride semiconductors is underway in Japan and overseas.

  What is important for producing the above-described highly efficient multi-junction solar cell is the concept of “current matching”. In an ordinary multi-junction solar cell, each solar cell to be joined is connected in series. Therefore, the current that can be taken out as a multi-junction solar cell is limited by the lowest current value among the currents generated in each solar battery cell. Therefore, the structure is designed to equalize the current generated in each solar battery cell. Thus, equalizing the current generated in each solar cell is called current matching, and is a condition necessary for realizing a highly efficient multijunction solar cell.

However, when a multi-junction solar cell composed of nitride semiconductor solar cells and silicon solar cells is to be manufactured, there is a current situation that it is difficult to achieve current matching. The silicon solar cell has a power generation efficiency of about 15% that is generally marketed and has a short-circuit current of about 30 mA / cm ² . On the other hand, even if the maximum power generation efficiency is obtained among the nitride semiconductor solar cells realized at present, the short-circuit current is at most 3 mA / cm ² , which is 1/10 that of silicon solar cells. Only below.

  The factors that cause the short circuit current to be reduced in this way are as follows.

  First, in order to obtain a nitride semiconductor InGaN crystal having a certain level of quality, it is necessary to use InGaN with a relatively low In composition (typically 20% or less). In this composition, the forbidden band energy of InGaN becomes a large value exceeding 2.5 eV. Therefore, in the solar cell using InGaN having the above composition, light in the energy range of 2.5 eV or more as photon energy can contribute to power generation among the solar energy. This is only 18% of the total solar energy, and the current decreases accordingly. On the other hand, in the case of silicon, a little less than 64% of solar energy contributes to power generation.

  Second, although it is a somewhat good quality InGaN, the crystal quality is much inferior to silicon. In InGaN crystals, crystal defects such as dislocations and point defects exist at high density. For this reason, carriers (electrons and holes) generated by light absorption are recombined through crystal defects. As a result, the above-described solar cell made of a nitride semiconductor can extract only a current value significantly smaller than a value that should theoretically be extracted.

L. Hsu et al., "Modeling of InGaN / Si tandem solar cells", Journal of Applied Physics, vol.104, 024507, 2008. L. A. Reichertz et al., "Demonstration of a III. Nitride / Silicon Tandem Solar Cell", Applied Physics Express, vol.2, 122202, 2009. R. Dahal et al., "InGaN / GaN multiple quantum well concentrator solar cells", Applied Physics Letters, vol.97, 073115, 2010. MAStan et al., "27.5% EFFICIENCY InGaP / InGaAs / Ge ADVANCED TRIPLE JUNCTION (ATJ) SPACE SOLAR FOR HIGH VOLUME MANUFACTURING", Proc. 29th IEEE Photovoltaic Specialists Conference, New Orleans, USA, pp.816-819, 2002.1060- 8371

  As described above, multi-junction solar cells composed of nitride semiconductor solar cells and silicon solar cells are in a situation where it is difficult to achieve current matching, and nitride solar cells having a small current value when forced to match. Therefore, there is a problem that the energy value of the silicon solar cell in the multi-junction solar cell cannot be utilized and the solar energy is wasted. The first problem related to current matching is not limited to the combination of a nitride semiconductor and silicon, but similarly occurs for multijunction solar cells using semiconductors with different band gap energies.

  If the area of the nitride semiconductor solar battery cell is made larger than the area of the silicon solar battery cell with respect to the problem related to the current matching described above, current matching can be achieved in a state where a larger current value can be obtained. However, in this configuration, the light transmitted through the nitride semiconductor solar cells outside the silicon solar cells does not contribute to power generation in the silicon solar cells, so that the energy of sunlight is still wasted. Become.

  The present invention has been made to solve the above-described problems, and an object thereof is to enable power generation without wasting solar energy much.

Solar power generation system according to the present invention includes a first solar cell is composed of a first semiconductor and sunlight is arranged on the incident side of the incident, composed of second semiconductor not the size of the first semiconductor than the band gap energy A second solar cell stacked on the first solar cell opposite to the incident side and having a smaller area than the first solar cell, and a first solar cell around the second solar cell And a solar thermal power generation unit that generates power by the heat of sunlight that has passed through the solar power.

  The solar power generation system includes a condensing unit that condenses sunlight transmitted through the first solar cells around the second solar cell, and solar thermal power generation by the heat of the sunlight collected by the condensing unit The power generation of the part may be performed. The condensing means may be a convex lens. Further, the condensing means may be a concave mirror.

  In the solar power generation system, the solar power generation system includes a condensing unit that condenses sunlight incident on the first solar cell, and the sunlight condensed by the condensing unit is incident on the first solar cell. Also good. Note that the light collecting means may be a Fresnel lens.

  As described above, according to the present invention, an excellent effect that power can be generated without wasting solar energy much is obtained.

FIG. 1 is a configuration diagram showing the configuration of the photovoltaic power generation system according to Embodiment 1 of the present invention. FIG. 2 is a configuration diagram showing the configuration of the photovoltaic power generation system according to Embodiment 2 of the present invention. FIG. 3 is a configuration diagram showing the configuration of the photovoltaic power generation system according to Embodiment 3 of the present invention. FIG. 4 is a configuration diagram showing the configuration of another photovoltaic power generation system according to Embodiment 3 of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Embodiment 1]
First, Embodiment 1 of the present invention will be described with reference to FIG. FIG. 1 is a configuration diagram showing the configuration of the photovoltaic power generation system according to Embodiment 1 of the present invention.

This solar power generation system includes a first solar cell 101 disposed on an incident side on which sunlight 111 from the sun 110 is incident, and a first solar cell 101 stacked on the first solar cell 101 opposite to the incident side. 2 solar battery cells 102. The first solar cell 101 is composed of a first semiconductor, the second solar cell 102 is composed of a second semiconductor have large band gap energy than the first semiconductor. For example, the first semiconductor is silicon and the second semiconductor is a nitride semiconductor. The second solar battery cell 102 has a smaller area than the first solar battery cell 101.

  The first solar battery cell 101 includes, for example, a p-type silicon layer and an n-type silicon light receiving layer formed on the p-type silicon layer. The surface on the p-type silicon layer side is the incident side on which sunlight 111 is incident. The second solar cell 102 includes an n-type nitride light-receiving layer made of an n-type nitride semiconductor (for example, InGaN) and a p-type nitride light-receiving layer made of a p-type nitride semiconductor (for example, InGaN). . These can be formed, for example, by crystal growth on a semiconductor substrate made of a nitride semiconductor. The n-type nitride light-receiving layer side is the first solar cell 101 side.

  In addition, the solar power generation system according to Embodiment 1 includes a solar thermal power generation unit 103 that generates power by the heat of sunlight 112 that has passed through the first solar battery cells 101 around the second solar battery cells 102. Moreover, in Embodiment 1, the convex lens (condensing means) 104 which condenses the sunlight 112 which permeate | transmitted the 1st photovoltaic cell 101 is provided, and electric power generation of the solar thermal power generation part 103 is carried out with the heat | fever of the condensed sunlight. Done. The solar power generation unit 103 includes a solar water power generation water layer 131, a turbine 132, and a generator 133.

  According to the solar power generation system in the first embodiment, the sunlight 111 incident near the center of the first solar cell 101 absorbs light on the short wavelength side in the first solar cell 101, and the second solar cell. Power is extracted by absorbing light on the long wavelength side in the cell 102. Here, as described above, by making the first solar battery cell 101 appropriately large in area with respect to the second solar battery cell 102, the amount of current generated in each cell can be made equal. The current matching condition can be satisfied.

  Next, sunlight that has entered the surrounding area from the second solar battery cell 102 is absorbed and transmitted only by the first solar battery cell 101 on the short wavelength side. Long wavelength sunlight 112 that has passed through the surrounding first solar cells 101 from the second solar cells 102 is collected by the convex lens 104 and heats the water contained in the solar power generation water layer 131. The heated water becomes high-temperature and high-pressure steam, and rotates the turbine 132. The generator 133 operates using the turbine 132 operating in this manner as a power source, and power is generated. Thus, the sunlight 112 which passed the surrounding 1st photovoltaic cell 101 from the 2nd photovoltaic cell 102 is utilized as energy for solar thermal power generation.

  As described above, according to Embodiment 1, electric power can be taken out without wasting solar energy much.

  By the way, in the above description, a two-junction solar cell including two solar cells is used. However, the present invention is not limited to this. For example, the first solar cell is made of InGaP, the second solar cell is made of Ge, and in addition, the third solar cell made of InGaAs between the first solar cell and the second solar cell. You may make it use the 3 junction solar cell which has arrange | positioned the battery cell (refer nonpatent literature 4).

  In this configuration, the first solar cell and the third solar cell generate substantially the same amount of current, and the generated current amount of the second solar cell is larger than these. Therefore, the first solar cell and the third solar cell may have the same area, the second solar cell may have a smaller area, and the amount of current between them may be equal. Even in this case, if solar power generation is performed in the same manner as described above using sunlight on the long wavelength side that has passed through the first and third solar cells surrounding the second solar cell, further solar energy is obtained. It is possible to increase the use efficiency.

[Embodiment 2]
Next, Embodiment 2 of the present invention will be described with reference to FIG. FIG. 2 is a configuration diagram showing the configuration of the photovoltaic power generation system according to Embodiment 2 of the present invention.

  This solar power generation system includes a first solar cell 101 disposed on an incident side on which sunlight 111 from the sun 110 is incident and a second solar cell 101 stacked on the first solar cell 101 opposite to the incident side. A solar battery cell 102. These configurations are the same as those in the first embodiment.

  The solar power generation system according to the second embodiment also includes a solar thermal power generation unit 103 that generates power using the heat of sunlight 112 that has passed through the first solar battery cells 101 around the second solar battery cells 102. The solar thermal power generation unit 103 is also the same as that of the first embodiment described above, and includes a solar thermal power generation water layer 131, a turbine 132, and a generator 133.

  In Embodiment 2, the concave mirror (condensing means) 204 which condenses the sunlight 112 which permeate | transmitted the 1st photovoltaic cell 101 is provided. In Embodiment 2, sunlight 112 is condensed by the concave mirror 204, and the water accommodated in the water layer 131 for solar power generation is heated. Other configurations are the same as those in the first embodiment.

  In the second embodiment described above, similarly to the first embodiment described above, electric power can be taken out without wasting solar energy much.

[Embodiment 3]
Next, Embodiment 3 of the present invention will be described with reference to FIG. FIG. 3 is a configuration diagram showing the configuration of the photovoltaic power generation system according to Embodiment 3 of the present invention.

This solar power generation system includes a first solar cell 301 disposed on an incident side on which sunlight 111 from the sun 110 is incident, and a first solar cell 301 stacked on the first solar cell 301 opposite to the incident side. 2 solar cells 302. The first solar cell 301 is composed of a first semiconductor, the second solar cell 302 is composed of a second semiconductor has a size of the first semiconductor than the band gap energy. For example, the first semiconductor is silicon and the second semiconductor is a nitride semiconductor. The second solar cell 302 has a smaller area than the first solar cell 301.

  The first solar cell 301 includes, for example, a p-type silicon layer and an n-type silicon light receiving layer formed on the p-type silicon layer. The surface on the p-type silicon layer side is the incident side on which sunlight 111 is incident. The second solar cell 302 includes an n-type nitride light-receiving layer made of an n-type nitride semiconductor (for example, InGaN) and a p-type nitride light-receiving layer made of a p-type nitride semiconductor (for example, InGaN). . These can be formed, for example, by crystal growth on a semiconductor substrate made of a nitride semiconductor. The n-type nitride light receiving layer side is the first solar cell 301 side.

  The solar power generation system according to Embodiment 3 includes a solar thermal power generation unit 103 that generates power by the heat of sunlight 112 that has passed through the first solar battery cells 301 around the second solar battery cells 302. Further, the third embodiment includes a Fresnel lens (condensing means) 304 that condenses sunlight 111 and a homogenizer 305 that makes the condensed light 312 collected by the Fresnel lens 304 uniform light. The Fresnel lens 304 has a convex shape toward the end of light. In addition, the condensed light 312 is made uniform in light power distribution by the homogenizer 305 and is incident on the first solar cell 301.

  In the third embodiment, as described above, the condensed light 312 is incident on the first solar cell 301, and the heat of the sunlight 314 transmitted through the first solar cell 301 around the second solar cell 302. Power generation by the solar thermal power generation unit 103 is performed. The solar power generation unit 103 is the same as in the first and second embodiments, and includes a solar water generation water layer 131, a turbine 132, and a generator 133.

  According to the solar power generation system in the third embodiment, the sunlight 313 collected by the Fresnel lens 304, made uniform by the homogenizer 305, and incident near the center of the first solar cell 301 is the first solar cell. The cell 301 absorbs light on the short wavelength side and the second solar battery cell 302 absorbs light on the long wavelength side to extract electric power. Here, in the same manner as in the first embodiment, the first solar cell 301 is appropriately increased in area with respect to the second solar cell 302 so that the amount of current generated in each cell is equal. Current matching conditions can be satisfied.

  Next, the sunlight 313 incident on the surrounding area from the second solar battery cell 302 is absorbed and transmitted only by the first solar battery cell 301 on the short wavelength side. The long wavelength sunlight 314 that has passed through the surrounding first solar cells 301 from the second solar cells 302 heats the water contained in the solar thermal power generation water layer 131. The heated water becomes high-temperature and high-pressure steam, and rotates the turbine 132. The generator 133 operates using the turbine 132 operating in this manner as a power source, and power is generated. Thus, the sunlight 314 which passed the surrounding 1st photovoltaic cell 301 from the 2nd photovoltaic cell 302 is utilized as energy for solar thermal power generation.

  As described above, according to Embodiment 3, electric power can be taken out without wasting solar energy much.

  Incidentally, a plurality of multi-junction solar cells including the first solar cell 301 and the second solar cell 302 may be used. As shown in FIG. 4, a plurality of sets including a Fresnel lens 304, a homogenizer 305, a first solar cell 301, and a second solar cell 302 are provided, and a plurality of sets of sunlight 314 are collected by a concave mirror 204 and collected. You may make it implement the electric power generation of the solar thermal power generation part 103 by heating the water accommodated in the water layer 131 for solar thermal power generation with the condensed light 315 which lighted.

  As described above, according to the present invention, the solar thermal power generation unit generates power with the heat of sunlight transmitted through the first solar cells around the second solar cells having a smaller area. It will be possible to generate electricity without wasting light energy too much.

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious.

  DESCRIPTION OF SYMBOLS 101 ... 1st photovoltaic cell, 102 ... 2nd photovoltaic cell, 103 ... Solar thermal power generation part, 104 ... Convex lens (condensing means), 110 ... Sun, 111,112 ... Sunlight, 131 ... Water layer for solar thermal power generation, 132 ... turbine, 133 ... generator.

Claims (6)

A first solar cell that is composed of a first semiconductor and disposed on an incident side on which sunlight is incident;
The configured from the second semiconductor has a size of the first semiconductor than the band gap energy, a second which is a smaller area than the first solar cell is laminated on the first solar cell opposite to the incident side Solar cells,
A solar thermal power generation system comprising: a solar thermal power generation unit that generates power by the heat of sunlight transmitted through the first solar battery cell around the second solar battery cell. The solar power generation system according to claim 1,
Condensing means for condensing sunlight transmitted through the first solar cells around the second solar cells,
The solar power generation system is characterized in that the solar thermal power generation unit generates electric power by the heat of sunlight condensed by the light collecting means. The solar power generation system according to claim 2,
The condensing means is a convex lens. The solar power generation system according to claim 2,
The condensing means is a concave mirror. The solar power generation system according to claim 1,
Condensing means for concentrating sunlight incident on the first solar cell,
Sunlight condensed by the condensing means is incident on the first solar cell. The solar power generation system according to claim 5,
The condensing means is a Fresnel lens.

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